The present invention relates to an electromagnetically-operated fuel injection valve for use in an electronically-controlled fuel injection system.
In an electronically-controlled fuel injection system for an internal combustion engine of an automotive vehicle, an electromagnetically-operated fuel injection valve has been used.
As disclosed in Kamai et al U.S. Pat. No. 4,331,317 assigned to the same assignee of the present application, for instance, the fuel injection valve generally has an electromagnetic coil wound on a stator core in a valve casing, an armature core integrally connected with a valve needle for opening and closing an injection port, and a spring disposed between the stator core and the armature core for biasing the valve needle to close the injection port. While the electromagnetic coil is energized, a magnetic circuit is formed through the stator core, the valve casing, the armature core and an air gap between the stator core and the armature core, and the armature core is attracted against the biasing force of the spring so that the valve needle integral with the armature core opens the injection port for metering fuel.
In the magnetic circuit, the minimum cross-sectional area for the magnetic flux is formed at a portion where the bottom of the stator core and the top of the armature core face with the air gap therebetween and the cross-sectional area for the magnetic flux in the other portions of the magnetic circuit is made larger than the minimum cross-sectional area. As a result, while the electromagnetic coil is kept energized, the electric current actually flowing through the electromagnetic coil and the resulting electromagnetic force increase gradually until the magnetic saturation occurs, even after the armature core and the valve needle are fully attracted to open the injection port fully after a valve opening response delay. Since the time period the electromagnetic coil is kept energized is varied in proportion to the required quantity of fuel, the electric current having been flowing through the electromagnetic coil and the electromagnetic force generated just before the electromagnetic coil is deenergized is dependent on the time period the electromagnetic coil has been energized. As a result, a valve closing response delay in which the valve needle is returned to the fully closed position from the fully open position in response to the deenergization of the electromagnetic coil is varied in dependence on the energization time period. Therefore, even if the valve opening response delay is substantially constant, linearity between the energization time period and the metered quantity of fuel cannot be assured.